The Archean sediments of the southern Canadian Shield are mainly graywacke. Much conglomerate, a little slate, and still less iron-bearing formation are also present. Excessive thickness, especially of the conglomerates, abundance of graded bedding, rarity of cross-bedding and absence of ripple mark, the graywacke nature of the arenaceous beds, the absence of true quartzites and limestones and scarcity of normal argillaceous sediments, and the association with greenstones and tuffs are all the earmarks of a geosynclinal facies of sedimentation. The deposits are much like the rapidly accumulated “Flysch” sediments of later eras.

The petrology of the sediments of any age is determined primarily by the tectonic environment. Whether the deposit is marine or continental is of secondary importance. Deep erosion left only the axial portion of the Archean geosynelines and hence only orogenic sediments. In this fact is found an explanation of the petrographic similarity of all early pre-Cambrian sediments regardless of age (Timiskaming-type) and the differences between these sediments and those of most of the Huronian (Huronian-type) and later periods.

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